Gusev is halfway around the planet from the Meridiani region where Spirit's twin,
Opportunity, recently found evidence that water used to flow across the surface.

"This is not water that sloshed around on the surface like what appears to have
happened at Meridiani. We're talking about small amounts of water, perhaps
underground," said Dr. Hap McSween, a rover science team member from the University of
Tennessee, Knoxville.

"The evidence is in the form of multiple coatings on the rock, as well as fractures
that are filled with alteration material and perhaps little patches of alteration
material," McSween said during a press conference at NASA's Jet Propulsion Laboratory,
Pasadena, Calif.

The rock, called "Mazatzal" after mountains in Arizona, lies partially buried near the
rim of the crater informally named "Bonneville" inside the much larger Gusev Crater.
Its light- toned appearance grabbed scientists' attention. After Spirit's rock
abrasion tool brushed two patches on the surface with wire bristles, a gray, darker
layer could be seen under the tan topcoat. The rock abrasion tool ground into the
surface with diamond cutting teeth on March 26. Then, after an examination of the
newly exposed material, it ground deeper into the rock two days later. A lighter-gray
interior lies under the darker layer, and a bright stripe cuts across both.

Dr. Jeff Johnson, a science team member from the U.S. Geological Survey's Astrogeology
Team, Flagstaff, Ariz., said the stripe "seems to be a fracture that water has flowed
through, potentially with minerals precipitating from that fluid and lining the walls
of the crack."

He and other scientists stressed that the interpretations are preliminary. "The team
is, as always, trying to find time to digest these observations while also preparing
for the next day's operations," Johnson said.

Spirit's alpha particle X-ray spectrometer checked what chemical elements were close
to the surface of untreated, brushed, once-drilled and twice-drilled patches.
"Miracles, miracles, miracles. We have a lot of work to do," the instrument's lead
scientist, Dr. Rudi Rieder of the Max Planck Institute, Mainz, Germany, exclaimed
about the results. For example, the ratio of bromine to chlorine seen inside the rock
is unusually high and possibly a clue to alteration by water.

The final experiment on Mazatzal was to scrub the surface with the rock abrasion tool
in a pattern of five circles arranged in a ring, with a sixth circle in the center.
Besides creating a rock-art daisy, this task by the engineers of New York-based
Honeybee Robotics, as well as JPL, produced a brushed patch big enough to fill the
field of view of Spirit's miniature thermal emission spectrometer, said Dr. Steve Ruff
of Arizona State University, Tempe. The tan outer surface appears to have a
strikingly different mineral composition than the dark gray coating exposed by the
brushing, but more time is needed to complete the analysis, he said.

McSween proposed that the light outer coat, dark inner coat and bright veins could
have resulted from three different periods of the rock being buried, altered by fluids
and unburied.

While scientists await transmission of additional data Spirit has collected about
Mazatzal, the rover will be making its way toward the "Columbia Hills" about 2.3
kilometers (1.3 miles) away. Spirit left the rock and drove 36.5 meters (120 feet)
early Thursday.

Opportunity set a one-day driving record on Mars on March 27 by covering 48.9 meters
(160 feet) toward a rock called "Bounce Rock" because airbag bounce marks show that
the spacecraft hit it on landing day two months ago. "We're looking to break that
record again very soon with longer and longer drives," said JPL's Chris Lewicki,
flight director.

Before moving on across the plains of Meridiani, though, Opportunity will complete an
investigation it has begun of Bounce Rock. The rock is unlike any seen on Mars before,
said Dr. Jim Bell, lead scientist for the rovers' panoramic cameras. "There are some
shiny surfaces on this rock," he said, describing them as "almost mirrorlike."

The two rovers' 18 cameras have now taken more than 20,000 images. JPL, a division of
the California Institute of Technology in Pasadena, manages the Mars Exploration Rover
project for NASA's Office of Space Science, Washington, D.C.